Hurtling Toward Mars

August
21, 2007: By the time you finish reading this sentence,
you'll be 25 miles closer to the planet Mars.

Earth
and Mars are converging, and right now the distance between
the two planets is shrinking at a rate of 22,000 mph--or about
25 miles per sentence. Ultimately, this will lead to a close
approach in late December 2007 when Mars will outshine every
star in the night sky. Of a similar encounter in the 19th
century, astronomer Percival Lowell wrote the following: "[Mars]
blazes forth against the dark background of space with a splendor
that outshines Sirius and rivals the giant Jupiter himself."

Contrary
to rumor, though, Mars is never going to outshine the Moon.

There
is an email circulating the internet—called the "Mars
Hoax" or the "Two Moons email"—claiming that
Mars will soon swell as large as the full Moon, and the two
will hang together side by side on the night of Aug. 27th.
"Mars will be spectacular," it states. "No
one alive today will ever see this again."

It
is true that Earth and Mars are converging--you're
now 300 miles closer--but even at closest approach the two
planets are separated by a gulf of tens of millions of miles.
From such a distance, Mars looks like a star, an intense yet
tiny pinprick of light, never a full Moon.

To
appreciate the situation, think of Earth and Mars as runners
on a track, with speedy Earth on the inside lane and slower
Mars on the outside: diagram.
Now, in August, Earth is catching up to Mars from behind. Relative
speed: 22,000 mph. In December, Earth overtakes Mars, still
moving rapidly but never approaching the Red Planet any nearer
than the gap between lanes: about 55 million miles.

Mindful
that the two planets are converging, NASA chose this time
to send its Phoenix
Lander to Mars. Launched on Aug. 4, 2007, from Cape Canaveral,
Phoenix is slated to land in late May 2008 on a Martian arctic
plain where Phoenix's robotic arm will dig in the dirt hunting
for, among other things, habitats for microbial life. Only
to Phoenix, when it gets very close to Mars next year, will
the red planet actually rival the Moon in apparent size.

So
… you should forget about Mars on August 27th, right?

Not
so fast. While there won't be Two Moons on August 27th, there
will be Two Eyes. At 3 o'clock in the morning on that date,
Mars will rise in the eastern sky alongside the red giant
star Aldebaran. The two red lights side-by-side will resemble
two eerie, unblinking eyes. This is worth waking up for!

If
you've been following the adventures of Spirit and Opportunity,
you know that Mars is currently experiencing a planet-wide
dust storm. Rust-colored dust is choking the air and dimming
sunlight, causing problems for the two solar-powered rovers.
During the past month, they've had to "stand-down"—no
roving or digging or even communicating with Earth at times—in
order to conserve power. A
backyard telescope pointed at Mars on August 27th may reveal
vast clouds of dust partially eclipsing some of the planet's
familiar surface markings. Or it may reveal a totally orange
ball—that's what Mars looks like when the dust storm kicks
into high gear. Take a look; every night the view improves.

More
about the Mars Hoax -- The Mars
Hoax email first appeared in 2003. On August 27th
of that year, Mars really did come historically close
to Earth. But the email's claim that Mars would rival
the Moon was grossly exaggerated. Every August since
2003, the email has staged a revival; it is as wrong
now as it was then.

One
version of the 2003 email stated that Mars would resemble
a full Moon when viewed at 60x power through a backyard
telescope. Even that is wrong: While it is true that
Mars can be magnified enough to illuminate a Moon-sized
patch of retina, the human brain doesn't register a
Moon-sized object. The brain takes into account context
and surroundings when it estimates the size of an object--hence
the Moon illusion. Nothing seen through the narrow corridor
of a telescope's eyepiece feels or looks as large as
a full Moon.